At what time of year did the Celts believe the Sun stood still for 12 days?

The Celts associated the Sun standing still for 12 days with the winter solstice. The idea reflects the apparent pause in the Sun’s seasonal movement around the shortest days of the year, when sunrise and sunset positions change very slowly.

The winter solstice occurs when one hemisphere is tilted farthest away from the Sun. In the Northern Hemisphere it falls around December 21 or 22, producing the year’s shortest day and longest night. Afterward, daylight gradually begins increasing again.

The phrase “stand still” is the literal meaning behind solstice, from Latin solstitium: “Sun standing still.” Many later accounts connect midwinter customs, fires and extended celebrations with a solstitial turning point, although “the Celts” covered many cultures and centuries rather than one uniform religious tradition.

This answer is sometimes confused with Yule or the broader Twelve Days of Christmas. Those are seasonal festivals or calendars; the astronomical occasion named in the quiz is the winter solstice.